The present invention relates to manual gear shifting mechanisms for power transmissions such as multi-speed transmissions employed in automotive vehicles, and particularly relates to such transmissions having the final speed range as an overdrive.
In order to maintain the shift stick or lever pattern as a conventional progressive "H" type pattern for the forward speed ranges, it has been found necessary to reverse the internal shift fork movement for the final speed changes in order to provide for the overdrive speed range to be attained in the final position of the shift stick or lever. Heretofore, this reversing of the shift fork action within the transmission for the final speed change in an overdrive transmission has been accomplished by employing a pivoted lever or "flipper" between the shift stick and the shift fork to reverse the action of the shift stick on the movement of the shift fork to cause the shift fork to engage the direct drive ratio in the next to the final position, and the overdrive ratio engagement in the final position of the shift stick.
Known techniques for mounting a shift fork reversing flipper in a manually shiftable vehicle transmission have utilized an arrangement wherein the flipper was mounted above the shift rail array on the underside of the gear box cover. Typically, in such an arrangement the flipper or lever engages the final shift fork on one end of the lever and a slider block, mounted on another shift rail, engages the lever at the end opposite the lever pivot or fulcrum. This arrangement whereby the flipper engaged the slider and final shift fork on the opposite side of the shift rail array from the side of the rail array where the shift fork loads are applied has resulted in additive effects of the bending moments on the shift fork. This in turn has resulted in increases in the reaction loads on the shift fork hub where it is joined to its rail; and also has resulted in additive moments and reaction forces of the hub of the slider block which with respect to the rail upon which it is guided for movement. In some instances this increase in reaction to forces has caused binding of the block during shifting where the slider block has a narrow hub.
Referring to FIG. 7, a known arrangement of a shift fork reversing arrangement as employed for the final stage in an overdrive transmission is indicated generally at 10, wherein the transmission housing structure or cover 12 has a flipper or lever 14 pivotally mounted about the pin 16 attached to the housing 12 on the underside of the cover portion thereof. Plural shift rails, denoted 18,20,22, are slidably guided at their ends, respectively, for axial movement on the housing 12. The shift block 24 is shown as rigidly connected to rail 22 by screw 26 for movement therewith. Block 24 has lug 28 extending upwardly therefrom, which is notched to engage one end of lever 14. A portion of a shift yoke or fork 30 is illustrated for the final stage and as slidably received on rail 18, and has upwardly-extending lug 32 which is notched to engage the end of lever 14 on the opposite side of pin 16 from the lug 28. A shift block (not shown) connected to rail 22 is selectively engaged by a shift stick or lever (not shown); and, movement of shift block 24 in one direction along rail 22 results in movement of the yoke 30 in the opposite direction.
It will be seen by those familiar with automotive power transmissions that the bending moments on the shift yoke 30 are additive, resulting in increased reaction loads on the sliding surface of the yoke 30 on rail 18. This has resulted in increased wear of the parts and resilient deflection under load which can produce sloppiness on the shifting action.
In the prior art arrangement of an overdrive transmission shift mechanism employing a flipper as shown in FIG. 7, the Neutral positioning of yoke or fork 30 is provided by spring loaded ball detenting of rail 22. Thus the Neutral positioning of yoke 30 is subject to tolerance accumulations of the engagement of lever 14 with block 24, location and fit on pin 16, and engagement of lever 14 in the notch in lug 32 on yoke 30. This tolerance accumulation in the prior art has caused sloppiness of shift action and Neutral positioning of yoke 30.
It has thus been desired to provide for conventional H type shift pattern in a multi-speed transmission having an overdrive final shift position, and to provide for long life of the shifting mechanism and precision shift action.